Buggy code:
public class MockDirectoryWrapper extends Directory { final Directory delegate ; long maxSize ; long maxUsedSize ; double randomIOExceptionRate ; Random randomState ; boolean noDeleteOpenFile = true ; boolean preventDoubleWrite = true ; boolean trackDiskUsage = false ; private Set < String > unSyncedFiles ; private Set < String > createdFiles ; volatile boolean crashed ; Map < Closeable , Exception > files = Collections . synchronizedMap ( new IdentityHashMap < Closeable , Exception > ( ) ) ; Map < String , Integer > openFiles ; private synchronized void init ( ) { } public MockDirectoryWrapper ( Directory delegate ) { } public void setTrackDiskUsage ( boolean v ) { } public void setPreventDoubleWrite ( boolean value ) { } @ Deprecated @ Override public void sync ( String name ) throws IOException { } @ Override public synchronized void sync ( Collection < String > names ) throws IOException { } @ Override public String toString ( ) { } public final synchronized long sizeInBytes ( ) throws IOException { } public synchronized void crash ( ) throws IOException { } public synchronized void clearCrash ( ) throws IOException { } public void setMaxSizeInBytes ( long maxSize ) { } public long getMaxSizeInBytes ( ) { } public long getMaxUsedSizeInBytes ( ) { } public void resetMaxUsedSizeInBytes ( ) throws IOException { } public void setNoDeleteOpenFile ( boolean value ) { } public boolean getNoDeleteOpenFile ( ) { } public void setRandomIOExceptionRate ( double rate , long seed ) { } public double getRandomIOExceptionRate ( ) { } void maybeThrowIOException ( ) throws IOException { } @ Override public synchronized void deleteFile ( String name ) throws IOException { } private synchronized void deleteFile ( String name , boolean forced ) throws IOException { } @ Override public synchronized IndexOutput createOutput ( String name ) throws IOException { } @ Override public synchronized IndexInput openInput ( String name ) throws IOException { } public final synchronized long getRecomputedSizeInBytes ( ) throws IOException { } public final synchronized long getRecomputedActualSizeInBytes ( ) throws IOException { } @ Override public synchronized void close ( ) throws IOException { if ( ( openFiles ) == null ) { openFiles = new HashMap < String , Integer > ( ) ; } if ( ( noDeleteOpenFile ) && ( ( openFiles . size ( ) ) > 0 ) ) { Exception cause = null ; Iterator < Exception > stacktraces = files . values ( ) . iterator ( ) ; if ( stacktraces . hasNext ( ) ) cause = stacktraces . next ( ) ; <START_BUG> throw new RuntimeException ( ( "MockRAMDirectory:<seq2seq4repair_space>cannot<seq2seq4repair_space>close:<seq2seq4repair_space>there<seq2seq4repair_space>are<seq2seq4repair_space>still<seq2seq4repair_space>open<seq2seq4repair_space>files:<seq2seq4repair_space>" + ( openFiles ) ) , cause ) ; <END_BUG> } open = false ; delegate . close ( ) ; } boolean open = true ; public synchronized boolean isOpen ( ) { } public static class Failure { public void eval ( MockDirectoryWrapper dir ) throws IOException { } public MockDirectoryWrapper . Failure reset ( ) { } protected boolean doFail ; public void setDoFail ( ) { } public void clearDoFail ( ) { } } ArrayList < MockDirectoryWrapper . Failure > failures ; public synchronized void failOn ( MockDirectoryWrapper . Failure fail ) { } synchronized void maybeThrowDeterministicException ( ) throws IOException { } @ Override public synchronized String [ ] listAll ( ) throws IOException { } @ Override public synchronized boolean fileExists ( String name ) throws IOException { } @ Override public synchronized long fileModified ( String name ) throws IOException { } @ Override public synchronized void touchFile ( String name ) throws IOException { } @ Override public synchronized long fileLength ( String name ) throws IOException { } @ Override public synchronized Lock makeLock ( String name ) { } @ Override public synchronized void clearLock ( String name ) throws IOException { } @ Override public synchronized void setLockFactory ( LockFactory lockFactory ) { } @ Override public synchronized LockFactory getLockFactory ( ) { } @ Override public synchronized String getLockID ( ) { } @ Override public synchronized void copy ( Directory to , String src , String dest ) throws IOException { } }

Fix:
throw new RuntimeException ( ( "MockDirectoryWrapper:<seq2seq4repair_space>cannot<seq2seq4repair_space>close:<seq2seq4repair_space>there<seq2seq4repair_space>are<seq2seq4repair_space>still<seq2seq4repair_space>open<seq2seq4repair_space>files:<seq2seq4repair_space>" + ( openFiles ) ) , cause ) ;